Acute or plastic changes in brain function can be safely induced in humans by low-intensity electrical stimulation by delivering current through electrodes on a patient's scalp. Such electrical stimulation is sometime referred to as Neurocranial electrostimulation (NCS). These changes can be potentially used for therapeutic or performance enhancing applications. Currently available devices and techniques tend to be rudimentary, untargeted, inefficient, and/or unsafe. In a typical technique, stimulation is provided through one or more pairs of relatively-large, sponge-like electrodes.
Transcranial electrical stimulation generally refers to short-duration (e.g., 50-500 μs) of supra-threshold pulses (e.g., 100-1200 V). Cranial electrotherapy stimulation (CES) generally utilizes a range of waveforms with peak current levels ranging from 50 μA to 5 mA. Supra-threshold current pulse trains (about 0.9 A) are generally used during electroconvulsive therapy (ECT). DC waveforms ranging from about 260 μA to 2 mA are sometimes used for transcranial direct current stimulation (tDCS).
Transcranial AC stimulation uses AC currents.